Method and apparatus for recording a single video frame

ABSTRACT

A disc recorder having a single magnetic pick-up and record head and having a magnetic disc, rotating at the frame rate of a video signal, records and provides for display of a single frame from a video signal consisting of a series of video frames. Motion jitter is eliminated by recording on the disc recorder one of the two fields which make up a chosen video frame and then reproducing this field. The reproduced field signal is then stored and rerecorded onto the magnetic disc at a position relative to the original field recording corresponding to the delay between two interlaced fields. A memory having less capacity than that required for storing a complete field signal is used with only a portion of a field being reproduced, stored and rerecorded during each rotation of the magnetic disc. A complete video frame is thus recorded, ready for display, in which the two interlaced fields are identical.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Pat. application Ser.No. 635,671, filed Nov. 26, 1975, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to magnetic recorders and recording methods andespecially to such recorders adapted to be used to record and reproduceindividual video frames for stop-action or slow motion video display.The standard for video signals currently used in the United Statesrequires that a scanning pattern of 525 horizontal scanning lines perframe be utilized. A complete frame consists of two interlaced fields,the first field including the even numbered lines and the second fieldincluding the odd numbered lines in the picture scan. All of the linesin the first field are scanned in succession before the lines in thesecond field are scanned.

Magnetic disc recorders have in the past been used to produce highresolution images of single video frames. An individual frame may bereproduced repeatedly and supplied to a monitor so that a stop-actioneffect is created. Successive video frames each may be supplied to avideo monitor a number of times to create a slow motion effect. If thesubject portrayed in the video frame is in rapid motion, however, thefirst and second fields may differ significantly and interlaced displayof these fields may therefore cause significant distortion. An effectknown as motion jitter may occur due to the spatial displacement of thesubject during the elapsed time between the two interlaced fields.

One approach to this problem has been to record only one field and todisplay this field repeatedly at the field rate. A frame thus wouldconsist of only one field which is displayed twice in interlacedfashion. As shown in U.S. Pat. No. 3,636,253 to Notani et al., issuedJan. 18, 1972, this may be accomplished by using a field recorder inwhich one field is recorded during one full rotation of the magneticdisc. A frame is developed by reproducing the field signal twice and bydisplacing the second reproduced field by one-half horizontal line scantime from the first reproduced field to create the proper conditions forinterlace. Since the first and second fields are identical, however,vertical resolution is needlessly sacrificed in displaying stillsubjects or subjects which are moving relatively slowly.

To allow for high vertical resolution in the case of still subjects andjitter-free operation in the case of rapidly moving subjects, twomethods have previously been utilized. The first method is to requirethe disc recorder to operate at two rotational speeds. If a rapidlymoving subject is to be displayed, the recorder is operated at the fieldrate with one field repeatedly displayed in interlaced fashion. If astill or slowly moving subject is displayed, however, the disc recorderis operated at the frame rate with both fields of a frame being recordedand displayed. This method of operation is difficult to achieve andrelatively expensive. The disc drive servo-mechanism for two speedoperation is complicated and sophisticated controls are required.Further, differences in dynamic performance of the recorder at the twospeeds must be considered, both in the case of flying head hard discrecorders and in the case of flexible disc recorders.

A second method shown in U.S. Pat. No. 3,518,366 to Phan, issued June30, 1972, involves rerecording one field of a frame twice on a framerecorder. To accomplish this, a frame recorder is modified by providinga second recording head precisely displaced from the first head. The twomagnetic heads then record the single field simultaneously and one headis used for playback of the frame. If the disc is a multi-track disc, anadditional stepper mechanism is required for the extra head. This methodmay also be costly and complicated and may cause excessive disc wear.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus forrecording and displaying one frame in a video signal comprised of asuccession of frames, in which each frame includes two interlacedfields, are provided in which motion jitter is eliminated. A singleframe signal is recorded by a disc recorder rotating at the frame rate.Portions of a field of the recorded frame signal are reproduced andstored in a memory means. The stored signal is rerecorded by the discrecorder at a location on the disc in relation to the originallyrecorded field signal corresponding to the time delay between theinitiation of two successive fields. Only a portion of the single fieldsignal is reproduced, stored and rerecorded during each rotation of thedisc recorder, and therefore a plurality of rotations are required tocompletely rerecord the single field signal. The two field signalsrecorded on the disc recorder are reproduced and supplied to a monitorsuch that a video frame consisting of two identical interlaced fields isdisplayed.

It is therefore an object of the invention to provide a method ofrecording and a disc recorder in which a single field signal may berecorded twice to constitute the two interlaced fields of a frame; toprovide such a recorder in which only one recording head is necessary;further, to provide such a recorder in which operation of the recorderis at the frame rate of the video signal; to provide such a recorder inwhich a single field signal, having been recorded, is thereafter storedand rerecorded by the disc recorder to constitute the second interlacedfield; and to provide such a recorder in which only a portion of therecorded single field signal is stored and rerecorded on each rotationof the disc recorder, and in which complete rerecording of the singlefield signal requires a plurality of rotations of the disc recorder.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of the standard interlaced video scanningpattern;

FIGS. 2A and 2B are representations of portions of a video signal;

FIG. 3 is a simplified diagrammatic representation of the preferredembodiment of the invention;

FIG. 4 is a schematic representation of the circuit arrangement of thepresent invention;

FIG. 5 is a schematic representation of the circuit for the odd/evenfield descriminator of FIG. 4; and

FIGS. 6 and 7 are timing diagrams useful in explaining the operation ofthe device shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown in diagrammatic form thestandard interlaced scanning pattern utilized for video signals in theUnited States. The video signal consists of a succession of videopictures or frames which are presented at the rate of 30 per second.Each frame is made up of a number of horizontal scan lines with theUnited States standard being 525 lines per frame. As shown in FIG. 1,each horizontal line is slightly inclined to the right. This occursbecause during the scanning process a vertical deflection signal isgenerated which moves the scanning beam from the top of the picture tothe bottom of the picture at a constant rate. The horizontal deflectionis much more rapid and acts to move the scanning beam from left to rightto scan a line and then very rapidly to return the beam to the left edgeof the picture to begin the scan of the next succeeding line in thefield.

As seen in FIG. 1, each frame consists of two fields. Each odd numberedfield begins at point 20 and ends at point 25. After an odd numberedfield is scanned, the scanning beam is returned by a vertical deflectionsignal to point 30 where an even numbered field scan is begun. The evennumbered field scan ends at point 35 and the scanning beam is thenreturned to point 20 for the initiation of the scan of the next oddnumbered field.

Referring now to FIGS. 2A and 2B, two portions of a standard videosignal are shown. FIG. 2A illustrates the end of an even field, thebeginning of an odd field, and the vertical blanking between the fields.FIG. 2B is similar to FIG. 2A except that the end of an odd field andthe beginning of an even field are shown. As seen in FIG. 2A, thescanning beam intensity for each line is provided by a wave form such asthat indicated at 40. A level 45 is reached by the signal when a whiteportion of the line is scanned and a level 50 is reached by the signalwhen a black portion of the line is scanned. Timing information isprovided on the video signal by a series of pulses, the amplitudes ofwhich are not within the range used to specify the intensity of thebeam.

Specifically, horizontal sync pulses, such as pulse 55, are provided tosynchronize the horizontal beam deflection circuit in the video monitorwith the video information supplied to the video monitor. Each of thesepulses is outside the limits of the video beam intensity signal and,therefore, the picture displayed by the monitor is unaffected.

Between each field is a vertical sync pulse, shown at 60. The verticalsync pulse is serrated at 61, 62, 63, 64, 65 and 66 so that thehorizontal deflection circuit is provided with information allowing itto remain synchronized with the incoming video signal. During the timeperiod between fields, the scanning beam is returned to the top of thepicture in preparation for scanning the next field. The vertical syncpulses are repeated at the field frequency of 60 per second and like thehorizontal sync pulses, are of an amplitude which will leave the pictureunaffected. Before and after the vertical sync pulse 60, sixequalization pulses are provided in the equalization pulse intervals.The equalization pulses and serration pulses 61-66 appear at twice thehorizontal line rate.

A comparison of FIGS. 2A and 2B indicates that differences exist insignal timing between even and odd fields. Specifically, when comparedwith the timing of each vertical sync pulse, the horizontal sync pulsesused during an odd field are out of phase with the horizontal pulsesused during an even field by an amount equal to one-half of a line scan.Since the initial line scan of an even numbered field is only one-halfof a line and since, as seen in FIG. 1, the even and odd fields start atthe same vertical position, this half line phase difference will causeeach of the even field lines to be positioned exactly midway between twoadjacent odd field scan lines.

Referring now to FIG. 3, there is shown the preferred embodiment of theinvention. Disc recording means 70 includes a magnetic disc 71 and amagnetic pick-up and record head 75. Record head 75 may be positioned bya device such as that disclosed in U.S. Pat. No. 3,814,441, issued June4, 1974, to Craggs. The recording disc may be mounted as shown in U.S.Pat. No. 3,840,897, issued Oct. 8, 1974, to Kelley et al. or U.S. Pat.No. 3,737,880, issued June 5, 1973, to Kelley. Magnetic disc 71 isrotated with respect to pick-up head 75 by a means for rotating themagnetic disc at the frame rate of 30 rps. Such means may include thedisc drive devices disclosed in U.S. Pat. No. 3,814,844, issued June 4,1974, to Waldspurger et al. and U.S. Pat. No. 3,883,090, issued May 13,1975, to Hall. A source of video signal 78 supplies a video signal,consisting of a successive of video frames, to record electronics 80which are of standard design. Switches 85 and 86 comprise a switchingmeans which is initially set with both switches in their A positions.Although illustrated for the sake of simplicity as mechanical switches,switches 85 and 86 will be implemented by means of simiconductorswitching arrangements or equivalent high speed switching devices.

When the preferred embodiment of the present invention is operating, aframe comprised of two interlocked fields, will be recorded on disc 71.When it is desired to record and display a single frame, comprised oftwo identical fields, from the video signal, the timing logic 88 isactuated and causes switches 85 and 86 to switch into their respective Bpositions. One of the two interlocked fields recorded on disc 71 is thenreproduced by pick-up head 75 and standard reproduce electronics 90. Thereproduced field signal is supplied via line 91 to a delay or buffermemory means 95 which stores a portion of the signal. Memory 95 may bein the form of a charge transport device such as a charge coupleddevice, a bucket brigade, charge injection device, or a MOS diode array.Alternatively, the memory may be digital with an analog-to-digitalconverter at the input and a digital-to-analog converter at the output.

After a portion of the field has been stored in the buffer memory 95,switch 86 is returned to its A position and the stored field informationis then reapplied to record electronics 80 via line 98. The storedportion of the field is applied through switch 86 to the record head 75and recorded by disc recorder 70. A portion of the field signal is thenrerecorded during each of a plurality of successive rotations of thedisc recorder until the entire field signal has been rerecorded. Thetiming of this rerecording is such that the rerecorded field is recordeddirectly over the second of the two interlaced fields previouslyrecorded. The recording in FM erases the previously recorded signals.Thus the same field signal will be recorded on disc 71 as both the firstand the second field of a frame. Switch 86 may then be switched into itsB position and the recorded frame supplied to monitor 100 where theframe may be displayed. Since the first and second fields of the frameare identical, no motion jitter will occur.

The storage capacity of the memory determines the speed of thererecording operation. If the memory has a capacity of N lines, N linesmay be rerecorded during each rotation of the disc. Since there are, atmost, 245 active video lines per field, the number of disc rotationsrequired to rerecord a field would be 245 divided by N (rounded off tothe next larger interger).

As mentioned previously, rerecording of the single field signal takesplace directly over a previously recorded field signal to time preciselythe rerecording process. The timing logic 88 and sync stripper 105 maymonitor the horizontal sync of the field to be replaced. Further thesesync signals of the original video signal may be left unmodified on disc71 with only the active line signal of the field to be rerecorded beingstored in memory. The logic will thus cause the stored lines to bererecorded onto the disc, replacing one for one the lines complementaryto this field.

The choice of fields for rerecording may be made on either afirst-come-first-serve basis or may be previously determined. The timinglogic may rerecord only even or odd numbered fields into complementarypositions. Operating in a mode where the field to be rerecorded isselected arbitrarily may require that the playback rerecord sequence becontrolled by one of two separate control circuits after it isdetermined whether an even numbered field or an odd numbered field is tobe rerecorded. As previously mentioned, there is a one-half horizontalline displacement between odd and even fields and this may serve as amethod of detecting which of the two fields has been chosen forrerecording.

If it is desired to increase the speed of operation, the storagecapacity of buffer memory 95 may be increased so that an entire fieldsignal is stored simultaneously. Such change would of course materiallyincrease the cost of the recording apparatus. With such a memory,however, the apparatus of FIG. 3 could also function as a field recorderhaving an expanded capacity. This would be accomplished by onlyrecording alternate fields on recording disc 71. Since rotation is atthe frame rate, two non-related fields would be stored on each circulartrack on the disc. When one of the recorded fields is to be viewed onmonitor 100, transducer 75 is moved to the appropriate track and switch86 is switched into its B position. The desired field signal is thensupplied to monitor 100 via reproduce electronics 90. This same fieldsignal is simultaneously fed via line 91 to buffer memory 95. The outputof buffer memory 95 may then be applied by a switching arrangement (notshown) to monitor 100. The second application of the field signal istimed so as to create the necessary conditions for interlace. Thus bystoring only alternate fields on the disc recorder, twice as many frameswould be available for reproduction with acceptable definition.

To prevent moire effects that may occur as one field is rerecorded overanother field, the disc 71 may be rotated initially with one field beingerased prior to initiating of the rerecording process. The erasure mayextend into the horizontal sync pulses so that the switching transientswhich occur as the FM modulator is turned on and off will be removedduring sync processing. The sync must not be completely erased.

Reference is now made to FIG. 4 in which a schematic representation ofthe circuit of the preferred embodiment of the invention is shown. Thedisc recorder 70 includes a single transducer head 75 which cooperatesto record on magnetic disc 71 in the manner previously discussed.Transducer head 75 is used for recording and playback on the disc. An FMmodulated video signal to be recorded is supplied to input A on line 110which provides an input for standard record driver electronics 117. Thesignal on line 110 will be continuously recorded on the disc 71 bytransducer head 75. Playback circuit 119 controls the playback of thevideo signals which have been recorded on disc 71. Playback circuitincludes an FM demodulator and amplifiers and is gated off by a signalon line 121.

When it is desired to rerecord a video field on the disc 71 to produce avideo frame having identical fields, the signal on input A is removedand a record pulse applied by appropriate circuitry to line 123. Thisresets counter 125 and sets flip-flop 127, enabling circuit operation ina manner to be described below. The playback circuit 119 will also beenabled such that the frame which has been recorded will be played backby electronics 119 and supplied to line 129.

Sync stripper 131 separates the vertical, horizontal and composite syncsignals from the video signals and applies them to lines 133, 135, 136,respectively. The vertical sync pulses on lines 133 will reset counter137, divide-by-N counter 139, and divide-by-12-divider 141. Thehorizontal sync pulses on line 135 are supplied to gate G₁ viadivide-by-N counter 139 and via divide-by-12 divider 141. The number Nis set to equal the number of video lines which are to be rerecordedduring each revolution of the recorder. Divider 141 supplies a highsignal on its output after receiving 12 input pulses. The horizontalsync pulses are also supplied to inverter 145 which disables AND gatesG₂ and G₃ upon receipt of each horizontal sync pulse.

Phase locked loop oscillator 147 with feedback divider 149 provides apulse train at the rate of Q times the horizontal sync frequency to gateG₂. Gate G₂, when enabled, supplies this high frequency output to abuffer memory 151 and counter 152. Buffer memory 151 may be a chargetransport memory or, alternatively, a digital memory with ananalog-to-digital converter at its input and a digital-to-analogconverter at its output. The pulse train output from gate G₂ controlsthe rate at which the video signal information is shifted through thebuffer memory 151. A conventional FM modulator 153 receives the outputfrom buffer memory 151 and supplies it to gate G₄. Counter 152 countsthe pulse train and supplies an output signal on line 154 after Q pulseshave been counted and the active portion of the video line reproduced.The output from inverter 145 resets counter 152 prior to each videoline.

The sync stripper 131 provides a composite sync signal on line 136 whichincludes both the vertical and horizontal sync information as well asthe equalization pulses and the serration pulses which occur during thevertical pulse interval. This composite signal is applied to odd/evenvertical interval discriminator 157 which also receives the verticalsync signal on line 159.

Discriminator 157 provides output pulses on lines 159 and 161 whichindicate when the odd and even fields of the recorded material are beingreproduced. Output 159 will remain high for the duration of each oddfield and go low for the duration of each even field. Similarly, output161 will go high during each even field and low during each odd field.Switch 163 is provided to permit the operator to choose whether the oddfield or the even field on the disc 71 is to be replaced with theopposite field information.

The output of the odd/even vertical interval discriminator 157 issupplied on line 165 to gates G₄ and G₅ and, on line 167, to the countinput of binary counter 125. The parallel outputs of counters 125 and137 are provided to digital comparator 169. When comparator 169 sensesthat the count in the two counters is equal, it provides an outputsignal on line 171. The count in counter 125, additionally, is sensed bydecoder 173 which provides a reset pulse to flip-flop 127 when counter125 reaches a count state equalling 242 divided by N.

The operation of the circuit of FIG. 4 is as follows. Initially, when anoperator determines that a frame is to be recorded, a single framesignal will be applied to input A and, via line 110, to the discrecorder 70. Since playback circuit 119 will not at this time beenabled, it will provide no signal to line 129. The disc recorder 70will now have recorded on a single track a frame signal consisting oftwo interlaced field signals. If the operator should determine that itis desirable to compose a video frame consisting of two interlaced,identical fields, the operator will actuate appropriate circuitry whichwill apply a pulse to line 123, thus resetting counter 125, whilesetting flip-flop 127. The Q output of flip-flop 127 will then go high.Playback circuit 119 will also receive a signal on its enabling input175. Such an enabling signal may conveniently be obtained from the Qoutput of flip-flop 127. A single video frame consisting of twointerlaced fields of non-identical video information will have beenrecorded on the disc 71. Switch 163 will have been set to either the oddor even switch position, thus determining which of the two fields is tobe replaced.

Assuming that an even field is then reproduced, the signal on line 165will be low and playback circuit 119 will not be inhibited by AND gateG₅. Circuit 119 will reproduce video signal stored by the recorder andapply this signal to line 129. Playback circuit 119 includes theappropriate standard FM demodulator and amplifiers. The video signalwhich is played back will be applied by line 129 to sync stripper 131and also to buffer memory 151. The line termination marked B at theinput of sync stripper 131 is connected to the line marked B on theinput of buffer memory 151. The buffer memory 151 will begin to storethe video signal.

Sync stripper 131 will separate the vertical, horizontal, and compositesync pulses from the video signal and apply them to lines 133, 135, and136, respectively. When the first vertical interval is reached, avertical sync pulse will be applied to line 133. The trailing edge ofthe vertical sync pulse will reset counter 137, divide-by-N counter 139,and divide-by-12 counter 141. After the vertical blanking interval, thehorizontal sync pulses applied to line 135 will be counted by divider141 and counter 139. After divider 141 has counted 12 horizontal syncpulses, and the divide-by-N counter 139 has counted N horizontal syncpulses, gate G₁ will be enabled.

Counter 137 will have been initially reset to a zero count. Counter 125will have also been reset but will have received a pulse on line 167such that it will be at a "one" count. Only the first set of N activelines of video will be clocked into the buffer memory 151, therefore.When the 8 bit counter 137 receives a second pulse from G₁, line 171from comparator 169 will be switched low and gates G₂ and G₃ disabled.Thus only the active lines of video information will be stored in thebuffer memory and the first twelve inactive lines ignored.

Assuming that the field from which these video horizontal lines weretaken was an even field, gate G₄ will be enabled by the odd/evenvertical interval descriminator 157 during the next vertical interval,just prior to the succeeding odd field. Counter 137 will be reset by thevertical sync signal to a zero count and thus digital comparator 169will provide a high output signal which will enable AND gates G₂ and G₃only after the recorder has reproduced the desired number of horizontallines and the counts in counter 137 and 125 are again equal. Inverter145 insures that only active portions of the video signal are stored inmemory 15 and rerecorded onto the disc. The stored lines of videoinformation will then be gated through gate G₄ and recorded onto thedisc recorder. The high signal on line 165 will be transmitted toinhibit playback circuit 119 during the rerecording process except wheninhibited by counter 152. Counter 152 will provide an output on line 154after each active line of video information; the previously recordedsync signals will therefore be applied to the line 129. The counter 137will thereafter increase its count by one, disabling comparator 171 andgates G₃ and G₂.

During the next revolution counter 125 will have been indexed such thatits count is increased by one. Counters 137 and 125 will be equal incount twice during this revolution but during the next successive groupof N horizontal video lines. Thus counter 125 will count the revolutionsof the disc recorder and counter 137 and digital comparator 169 willinsure that during each revolution a group of N horizontal lines isstored in the buffer memory 151 and then rerecorded onto the disc.

The decoder 173 is responsive to the count in counter 125 to provide areset pulse to flip-flop 127 when counter 125 reaches a count equal to242 (the number of active video lines) divided by N, rounded to the nextlarger integer. This will, by definition, occur after all the groups ofN horizontal lines have been properly rerecorded onto the disc at theappropriate locations.

Referring now to FIG. 5, the odd/even vertical interval descriminator157 is shown in greater detail. FIGS. 6 and 7 are pulse diagrams usefulin explaining the manner in which this circuit operates. Vertical syncsignals are applied to line 159 while the composite sync signals areapplied to line 136. Monostable multivibrator 179 is triggered by theleading edge of the vertical sync pulse. The multivibrator isnon-retriggerable provides a pulse on its output 181 which is equal induration to 75% of the horizontal line period. The output of monostablemultivibrator 179 is represented in FIGS. 6 and 7 as pulses 183.

Monostable multivibrator 185 receives the composite sync signal on line136 and provides on its output a series of pulses in phase with thehorizontal sync signal and at the horizontal sync frequency but having aduration of 75% of the horizontal line period. These pulses arerepresented in dashed lines in FIGS. 6 and 7 as pulses 187. The solidline pulses 189 illustrate the relative width of the horizontal syncpulses. The composite sync signals 191 are shown in FIGS. 6 and 7. Itshould be noticed that the vertical sync portion of the composite signalis broken by a plurality of serration pulses 193.

FIG. 6 indicates the relationship of the three pulse trains during thevertical interval just prior to an even field while FIG. 7 shows such atime relationship during the vertical interval just prior to an oddfield. A careful comparison of the relationship among the pulse trainsillustrated in FIGS. 6 and 7 will reveal that pulses 183', 193' and 187'in FIG. 6 will all be high simultaneously. In FIG. 7, however, pulse193' will not be coincident with any of the pulses 187.

If the three pulse trains are applied to an AND gate, such as AND gate195 in FIG. 5, the AND gate will supply pulse output at the beginning ofeach even field. The gate will, however, not provide such an output atthe beginning of each odd field. The output of gate 195 is supplied to aflip-flop 197 which changes state in dependence upon the signal appliedto its D input at the time it receives a clock input. AND gate 199combines the vertical sync pulse 183 with the composite sync signal 191such that it provides a high output at the first serration pulse of eachvertical interval. If an even field is about to occur, AND gate 195 willalso provide an output, thus causing flip-flop 197 to provide a highsignal on its Q output. If, on the other hand, an odd field is about tooccur, the flip-flop 197 will be clocked as AND gate 195 provides a lowoutput. Flip-flop 197 will therefore provide a high output on its Qoutput. Thus flip-flop 197 will provide complementary pulse trains inphase with the alternation between fields by the video disc recorder.

While the method herein described, and the form of apparatus forcarrying this method into effect, constitute preferred embodiments ofthe invention, it is to be understood that the invention is not limitedto this precise method and form of apparatus, and that changes may bemade in either without departing from the scope of the invention.

What is claimed is:
 1. A method of developing a frame signal from avideo signal comprised of a succession of frames, each frame includingtwo interlaced fields, comprising the steps of:recording a single framesignal on a disc recorder, said disc recorder including a singletransducer and a magnetic disc rotating at the rate of one rotation foreach frame in said succession of frames, producing one field signal ofthe recorded frame signal with said transducer and storing said fieldsignal, rerecording the stored single field signal on said discrecorder, and reproducing the two field signals recorded on said discrecorder whereby a frame signal consisting of two identical interlacedfields is provided.
 2. The method of claim 1 further comprising the stepof supplying said two field signals which were recorded on said discrecorder to a monitor whereby a frame consisting of two identicalinterlaced fields is displayed.
 3. The method of claim 2 in which only aportion of said one field signal including an integral number of linesis reproduced, stored and rerecorded during each rotation of saidmagnetic disc whereby a plurality of rotations of said disc recorder arerequired prior to reproducing the two field signals and supplying saidsignals to a monitor.
 4. A method of developing a single frame videosignal from a video signal consisting of successive frames, each of saidsuccessive frames consisting of two interlaced fields, and recordingsaid single frame video signal on a recorder having a moving magneticmedium and a single stationary transducer, said transducer defining anendless recording track on said medium during a complete cycle ofmovement of said magnetic medium, comprising the steps of:applying asingle field signal to said transducer and recording said single fieldsignal on said recording track, sensing the recorded single field signalwith said transducer and supplying said single field signal to a memory,storing said single field signal in said memory, reading out said singlefield signal from said memory and reapplying said single field signal tosaid transducer, and rerecording said single field signal on saidrecording track at a position on said track corresponding to the timedelay between two interlaced fields, whereby said single field signal isrecorded twice on said recording track and positioned so that the tworecordings of said single field signal are interlaced to comprise asingle frame signal.
 5. A method of developing a single frame videosignal from a video signal consisting of successive frames, each of saidsuccessive frames consisting of two interlaced fields and each of saidfields consisting of a plurality of lines, and recording said singleframe video signal on a recorder having a moving magnetic medium and asingle stationary transducer, said transducer defining an endlessrecording track on said medium as said medium moves past saidtransducer, comprising the steps of:a. applying a single field signal tosaid transducer and recording said single field signal on said recordingtrack, b. sensing a portion of the recorded single field signal withsaid transducer, said portion including an integer number of saidplurality of lines, c. storing the sensed portion of said single fieldsignal, d. rerecording said sensed portion of said single field signalon said medium at a location on said recording track with respect to theportion of the sensed portion of said single field signal correspondingto the time delay between the initiation of two successive fields, ande. repeating steps (b), (c) and (d) for successive portions of saidsingle field signal until said single field signal is rerecorded in itsentirety on said recording track in a position such that said singlefield signal comprises the interlaced fields of a video frame signal. 6.A stop-action recorder for recording a video signal and for providing ata frame rate to a monitor a video frame composed of two interlacedfields, without the motion jitter that results from spatial displacementof a subject during the time between display of the two interlacedfields, comprising:video source means for providing a signal to berecorded; disc means, including a magnetic disc and a magnetic pick-upand record head adjacent said magnetic disc, for recording a videosignal; means for rotating said disc at the rate of one revolution perframe; memory means for storing a signal applied thereto; switch meansfor applying one of said two interlaced field signals to said disc meansto be recorded on said magnetic disc during one-half revolution of saiddisc; means, connected to said head, for reproducing said one of saidtwo interlaced field signals recorded on said magnetic disc and forapplying the reproduced field signal to said memory means; and means,connected to said memory means, for reapplying said reproduced fieldsignal to said switch means whereby said one of said two interlacedfields is rerecorded by said disc means such that, in a subsequentdisplay of the signal recorded on said disc means, a frame composed oftwo identical interlaced fields will be shown by a video monitor.